TABLE E-1 Point Values of Input Parameters

Grams of Spores

m0

1 gm

Estimated Amount in Single Envelope Released in Mailroom

#/gram

ρ

1011

Spore without additive would be ca 1012/gram

Fraction aerosolized

f

0.2

Unknown

Air changes/hour

ACH

1

Based on common ventilation rates

Inhalation volume

V

2.4 m3

8 hours exposure at normal adult breathing rate

Dose–response parameter

k

7.16•10−6

From analysis of the Druett data on monkeys

Volume into which release occurred

Vroom

4290 m3

Based on floor plans, about 10% of the building volume comprised the mailroom

Individuals exposed

P

10

Based on 10% of the total estimated number of employees

When that concentration is multiplied by the inhalation volume for an exposure by an individual worker, the average number of spores inhaled (the dose) is computed as follows:

Using the best estimate for the dose–response relationship (in the exponential dose-response model), the risk (per individual exposed) is computed to be:

This computation suggests that all individuals so exposed should have contracted inhalation anthrax. However, it is obvious that several parameters and assumptions have gone into the production of this point estimate. If the uncertainties in each input were considered, what would be the estimated confidence limit for the number of persons who could have become ill?

There are two approaches to this assessment. In the first approach, all of the point estimates in Table E-1 are used and, in addition, an “effectiveness factor”



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